Known elevator installations, by way of example, generally consist of an elevator cage, a counterweight and a support means, which by way of a drive connects the elevator cage and the counterweight together. The elevator cage is moved in an elevator shaft by this drive by means of an elevator control. A measuring device which measures loading of the elevator cage is present in such an elevator installation. Such a load measuring device can serve the purpose of generating signals required for the elevator control and that are proportional to the load in order to avoid, for example, journeys with overload or unnecessary empty journeys. These load measuring devices are based on various principles.
WO 01/83350 describes a principle of a load measuring device for cable elevators, in which a single sensor generates a signal on the basis of the extent of deformation of a support carrying the elevator cage. The deformation of this support is caused by the total weight of the elevator cage. The resulting signal of the sensor is used as an input signal for an elevator control. A disadvantage of this principle can be that inaccuracies can arise caused by, for example, a temperature sensitivity of strain gauges employed in the individual sensor.
EP 0151949 B1 discloses a principle of a different load measuring device for elevator cages with strain gauges, in which such inaccuracies can be reduced. An elevator cage vertically guided in an elevator shaft is carried by a base frame with rectangular cross-section. Brackets onto which the cage floor is fastened are arranged at corners characterized by this cross-section. Loading of the cage floor leads to bending of a respective limb of these brackets. One of the strain gauges is in each instance fastened to opposite sides of this limb, which are loaded in bending or strain. The eight strain gauges are part of an electrical bridge circuit. A load-proportional signal generated with the help of the bridge circuit is communicated to an elevator control.
A possible problem with such a solution in that case is the high number of sensors and thus also the high number of signal connections within an evaluating circuit. Added to that is limited capability of access to the supports arranged under the elevator cage.